Devices for fibrillating sheet material

ABSTRACT

A rotatable drum having plural cutting elements over its surface, arranged in a manner to obtain a smaller transverse spacing between adjacent slits in the fibrillated material, than in previously proposed devices. Four different types of construction of drum are proposed each allowing for the particular arrangement of cutting elements.

O United States Patent 1 3,565,308

[7 2] lnventor Philip T. Slack [56] Ref n Cit d 21 A I N $5 32 UNITED STATES PATENTS E 18 1968 1,714,583 5/1929 Anthony s3/34sx [45] Patented Fe! 23 l97l 2,068,456 1/1937 Hooper 83/2X [73] Assi nee plasticisers Limmd 3,273,771 911966 Beaumont 225/3 g Dfighfington near Bradford Yorkshire 3,460,416 8/1969 Gilbert 225/97X England 3,474,611 10/1969 Suzuki et a1. 225/97X [32] Priority Feb. 14, 1968 Primary ExaminerJames M. Meister [33] Great Britain Attorney-Scrivener, Parker, Scrivener and Clarke [31] 7207/68 [54] DEVICES FOR FIBRILLATING SHEET MATERIAL 4 Claims, 9 Drawing Figs.

[52] US. 225/97, ABSTRACT: A rotatable drum having plural cutting elements 28]], 83/660 over its surface, arranged in a manner to obtain a smaller [51] Int. Cl 8261 3/00, transverse spacing between adjacent slits in the fibrillated B26f l/24 material, than in previously proposed devices. Four different [50] Field of Search 225/3, 93, types of construction of drum are proposed each allowing for the particular arrangement of cutting elements.

DEVICES FOR FIBRILLATING SHEET MATEL lation." It has been proposed to fibrillate film by passing the film over a rotating drum having a plurality of cutting edges or needles in spaced, staggered parallel relationship over its surface.

It is an object of the present invention to provide an improved fibrillator, by which a finer stranding of the fibrillated material can be obtained without loss of strength in the cutting elements.

In order to achieve small spacingbetween adjacent cuts it is necessary to utilize very thin cutting edges or needles,

hereinafter referred to as cutting elements since, where the cutting elements are in line the spacing between cuts cannot be less than the thickness of the cutting elements. Thus, where a cut spacing of 0.002 inches isrequired the cutting elements must not exceed 0.002 inches in thickness.

Cutting elements of this order of thickness tend to be very fragile and a fibrillator employing such elements is easily damaged. It is an object of the present invention to provide a fibrillator which is capable of achieving a small intercut spacing but in which the cutting elements need not be restricted in thickness to the desired spacing between cuts.

According to the present invention the cutting elements are arranged around the rotatable drum in axially parallel rows equally spaced therearound with the cutting elements in adjacent rows offset by a distance equal to the desired spacing between cuts. I

In order to prevent the fibrillated material from wrapping around the drum it is essential that the cutting elements do not act as claws as they withdraw from the cuts in the material. To this end the cutting elements must be inclined away from the normal to the drum surface, on the trailing side thereof. A preferred angle of inclination between the cutting elements and the normal to the drum surface at the base of the elements is found to be In one arrangement the cutting elements comprise needles soldered or welded to metal strips to form comblike assemblies with the needles equally spaced apart along the length of the metal strip. The metal strips are then inserted into axially parallel slots formed in the surface of the drum so that the needles protrude beyond the drum surface. In order that the needles are inclined to the surface of the drum the slots are formed at an appropriate angle. This type of fibrillator will be referred to as an N-type fibrillator;

In another arrangement the cutting elements comprise tapered pins secured in holes in the drum surface so as to leave the points of the pins projecting beyond the drum. The holes are arranged in axially parallel rows with the holes in adjacent rows offset by the required distance. As in the N-type fibrillator the holes in which the pins are secured are preferably inclined so that the protruding portion of the pins subtend the correct angle with the drum surface. This second arrangement will be referred to as a P-type fibrillator.

In a further arrangement a single or multistart helical thread is formed in the drum surface for example by milling or grindcutting blades. Each protrusion is cut away more on one side than on the other so that the cutting edge is displaced to one side or the other of the disc and the protrusions are ground alternately in this way around the disc. In this way an effective axial spacing between cutting elements can be obtained equal to half the thickness of the disc. This is of particular importance where axial spacing between the blades is required to be of the order of 0.002 inches since the discs can then be made from material of 0.004 inches thickness. In practice it is found that thinner material tends to be brittle and the discs are easily damaged. The disc cutters are sometimes referred to as segmented blades and in consequence this type of fibrillator will be referred to as an SB-type fibrillator.

The invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is an end view of an N-type fibrillator partly in section;

FIG. 2 is a plan view of a portion of the cylindrical surface of the N-type fibrillator of FIG. 1 unrolled to form a flat plain surface;

FIG. 3 is an end view of a part of a P-type fibrillator;

FIG. 4A is a view of one end of a GT-type fibrillator;

FIG. 4B is a view similar to FIG. 4A of an alternative GT- type fibrillator;

FIG. 5 is a plan view of a segmented disc for use in an S8- type fibrillator;

FIG. 6A is a sectional view taken along line A OF FIG. 5;

FIG. 6B is a sectional view taken along line 8 OF FIG. 5; and 1 FIG. 7 is a side view of a number of segmented blades sandwiched to form a fibrillator.

In FIGS. l and 2 of the drawings an end-type fibrillator is shown comprising a cylindrical body 10 mounted on an axle or shaft 12 for rotation about its axis. At regular intervals around the cylinder axially parallel slots [4 are formed in which lines of needles 16 are retained. As best seen in FIG. 2 the needles 16 are arranged close together with their points (shown diagrammatically at 19) in linear alignment with the slots 14.

In order to facilitate manufacture and replacement each line of needles is mounted on an elongate bar 20 for example by soldering or welding shown at 21, the assembly of needles and bar forming a comblike structure. Additional soldering or welding is applied between adjacent needles as shown at 22. Each comb forms an integral structure of needles and blades which is thereby readily replaceable should damage or wear occur.

The blade assemblies are secured in their respective slots by cover plates 24 which overliethe bars 20 and are screwed or other wise secured to the cylinder 10. In order that the surface of the cylinder is smooth the cover plates 24 are let into recesses adjacent the slots and formed by cutting away one wall of each slot. I

In order to prevent clogging or a clawing action, the needles 16 extend at an angle 0 (see FIG. 1) to the tangent to the cylinder at the line of contact of the line of needles with the cylinder. The angle 0 is such that the needles point away from the direction of rotation of the cylinder 10 so that instead of clawing their way out of the material the needles are withdrawn with little or no relative linear movement between the needles and material. (It will be seen that by defining 0 as the angle between the rear of the needle and the surface of the cylinder, the maximum value of 0 is In practice 6 will be considerably less than 90 and a preferred value of 6 is found to be 75-this is suitable for a 3-inch diameter drum having 36 lines of cutting elements arranged in sets of 6.

In order to provide staggering between adjacent lines of pins, spacers 26 are positioned at (say) the left-hand end of each slot 14. The left-hand ends of the slots 14 in FIG. 2 lie in the same radial plane and the spacers 26 are dimensioned so as to obtain the desired offset between each successive line of needles. For example where the spacing P (see FIG. 2) is 0.012 and it is desired to divide this spacing P by a factor of 6, five such spacers are required the first 0.002 inch thick, the

next 0.004 inch thick etc., the largest spacer being 0.010 inch thick. The seventh line of needles is in alignment with the first line of needles and in consequence no spacer is required for lines 1, 7 etc.

Although in the arrangement shown in the drawing only six lines of needles are shown, in practice a large number of lines of needles are used so that the speed of rotation of the fibrillator can be reduced. By arranging, for example, six sets of six lines of needles around the cylinder 10, the resulting fibrillator can be operated at one-sixth the rotational speed that would be necessary for the same fibrillator having only six lines of needles.

In FIG. 3 there is shown a P-type fibrillator which comprises hollow cylindrical shell 30 which forms a sleeve which can be fitted over a cylindrical bobbin 32. The bobbin 32 is preferably keyed to the sleeve 30 so that drive is transmitted between the two. The cutting elements are formed by pins 34 and the region around one of these pins 34 is shown in section to illustrate how the pins are retained in position. Each pin is conical in shape and is pushed into a tapered hole 36 formed in the wall of the sleeve 30. Each hole 36 tapers towards the outer surface of the sleeve 30 so that each pin 34 can only be introduced into a hole 36 from the inside of the sleeve 30. The length of the pin 34 and the angle of the taper is arranged to be such that the base of the needle lies substantially flush with the inside surface of the sleeve 30 so that the cylindrical bobbin 32 serves to keep the needles 34 in place, when inserted into the sleeve.

In accordance with the invention the tapered holes 36 are arranged in lines at regular intervals around the sleeve 30 with the holes in each line being offset by a predetermined distance (equal to the intercut spacing) from the corresponding holes in adjacent lines.

One end of one form of GT-type fibrillator is shown in FIG. 4A of the drawings. This comprises a cylindrical drum 40 having a multistart helical thread profile formed in its outer surface. Axially parallel slots 42 are formed in the surface of the drum 40 at regular intervals around the drum. The slots 42 cut right through the thread profile 44 and result in a line of cutting edges along either side of each slot 42 defined by the peaks of the thread profile. Since the thread follows a helical path the cutting edge defined by the peak of each thread profile and one slot 42 will be displaced axially from the corresponding cutting elements formed by the same thread profile peaks and the adjacent slots 42.

An alternative GT-type fibrillator is shown in FIG. 4B in which the bases of the slots 42 are inclined to the surface of the drum. In the embodiment shown the bases of the slots extend between the peaks of one line of cutting edges to the bases of an adjacent line of cutting edges.

FIGS. and 7 illustrate the component from which an SB- type fibrillator is built up and FIG. 7 illustrates part of a stack of such components which together form SB-type fibrillator. As best seen in FIG. 5, each component comprises a thin annular disc 20 having six radial protrusions 52 regularly spaced apart around its periphery. Each protrusion is ground or otherwise machined to form a cutting edge (as will be hereinafter described) so that the six protrusions 52 correspond to six cutting elements according to the invention By stacking a number of discs 50, as shown in FIG. 7, with the radial protrusions 52 in axial alignment, a fibrillator can be formed Holes 54 are preferably formed in the discs 50 so that when assembled, the discs can be held together, for example, by means of bolts, or rods passed through the aligned holes 54 and secured at each end for example by peening over.

In order to reduce the axial spacing between adjacent cutting elements, the protrusions 52 are ground in a particular way as will be explained with reference to FIG. 6. FIG.6A shows the protrusion immediately beyond the section line A while FIG. 6B. shows the protrusion immediately beyond section line B, of FIG. 5. Referring to FIG. 6A it will be seen that this protrusion is ground so that the cutting edge 56 is offset from the center of the disc thickness, the edge being formed by two equally inclined ground surfaces one of which extends over three-fourths of the thickness of the disc and the other of which only extends over a fourth of the thickness. On the other hand, the protrusion immediately beyond section line B 5 (and for that matter the next protrusion beyond the one shown in FIG. 6A) is ground so that the cutting edge 56 is offset towards the right-hand face of the disc and is also formed by two equally inclined ground faces, the left-hand one of which extends over three-fourths of the thickness of the disc. In this way the razor edge of each cutting element 52, is offset in opposite direction on alternate cutting elements.

As described with reference to the N-type fibrillator, more than one set of cutting elements can be arranged around the periphery of the fibrillator drum, so that the fibrillator can be rotated at lower speeds. Thus instead of six protrusions around the discs 50, 36 protrusions could be formed at intervals, the speeds of rotation of the resulting fibrillator requiring to be only one-sixth that of the fibrillator shown.

An N-type fibrillator embodying the invention was constructed as follows:

Drum of 3-inch diameter;

36 equally spaced axially parallel slots formed around the drum;

36 combs, each having a row of needles spaced at 0.0132- inch pitch. (re. 76 needles to the inch).

Lateral offset between adjacent rows in each set of six Rows l, 7, 13, 19, 25 and 31 start each set ofsix.

Angle of inclination of needles to drum surface 75.

Length of needles above drum surface 1 /32 inch.

It has been found that the factors which effect the geometry of the network which results from a fibrilliation process:

35 l. The linear speed of the film;

2. The linear speed of the fibrillator; 3. The length of the arc of contact of the film around the fibrillator; 4. The distance between adjacent cuts;

5. The distance around the fibrillator between each line of cutting elements; and 6. The distance by which the cutting element protrudes beyond the cylindrical surface of the fibrillator. For high speeds of fibrillation, long needles cause wrapping of the film around the fibrillator and in the P-type fibrillator the projecting length of the pins above the cylindrical surface should not exceed one-eighth of an inch and should preferably be one thirty-second of an inch. In practice therefore cutting elements which only project a short distance beyond the surface of the fibrillator are used and factor 6 (above) can be considered to remain constant.

From geometrical considerations a formula can be derived by which the relative speeds necessary in order to obtain a net- 5 5 work having particular dimensions can be calculated. Where it is desired to obtain a network in which the width of the uncut portions equals the -width of the cut portions, the formula is as follows:

a drum rotatable about its axis and cutaway to form a plurality of equally circularly spaced'apart axially parallel slots in the surface thereof;

a metal strip located in each slot and secured therein;

a plurality of needles secured to each metal strip to form a comb with the needles equally-spaced apart along the length of the strip and protruding beyond the surface of the drum; and

spacer means between the ends of the slots and the ends of the metal strips, whereby a staggering effect is obtained between the needles in adjacent combs.

2. A fibrillator as set forth in claim 1, wherein the cutting elements are inclined to the normal to the drum surface on the trailing side thereof.

3. A fibrillator as set forth inclairn 2 wherein the angle between each cutting element and the normal to the drum surface at the base of the element is 15.

4. A fibrillator as set forth in claim 1, wherein the slots are inclined to the surface of the drum so that the needles protrude therebeyond at an angle to the drum surface. 

1. A fibrillator for producing parallel slits in sheet material comprising: a drum rotatable about its axis and cutaway to form a plurality of equally circularly spaced apart axially parallel slots in the surface thereof; a metal strip located in each slot and secured therein; a plurality of needles secured to each metal strip to form a comb with the needles equally spaced apart along the length of the strip and protruding beyond the surface of the drum; and spacer means between the ends of the slots and the ends of the metal strips, whereby a staggering effect is obtained between the needles in adjacent combs.
 2. A fibrillator as set forth in claim 1, wherein the cutting elements are inclined to the normal to the drum surface on the trailing side thereof.
 3. A fibrillator as set forth in claim 2 wherein the angle between each cutting element and the normal to the drum surface at the base of the element is 15*.
 4. A fibrillator as set forth in claim 1, wherein the slots are inclined to the surface of the drum so that the needles protrude therebeyond at an angle to the drum surface. 